The present invention relates to a positive radiation-sensitive mixture containing a compound which forms an acid under the action of high-energy radiation, and an acid-cleavable compound.
In classical UV lithography, the resolution limit is determined by the wavelength of the radiation used. The constant decrease in feature sizes in chip production therefore requires new lithographic techniques for the sub-micron region, electron or X-ray radiation being employed because of their extremely short wavelength. At the same time, it has been shown that resist materials which are suitable as electron beam resists can also be employed as X-ray resist, and vice versa.
Known resist materials for this application are acrylates and methacrylates (G. M. Taylor, Solid State Technology, 124 (1984)). With these materials, sensitivity and structural resolution have been found to be usually contrary properties. In order for higher sensitivities to be achieved, halogens are usually incorporated into the resist. In this case, fluorine and chlorine are usually employed in positive resists, whereas it is usually bromine and iodine, besides chlorine, which are employed in negative resists (T. Yamaoka et al., Phot. Sci. Eng., 23: 196 (1979 )).
In general, negative resists exhibit higher sensitivity than positive resists, but, cannot simultaneously--as stated above--have a high resolution in the submicron region. On the other hand, positive methacrylate-based resists achieve high resolution, but, with the exception of polymethacrylonitrile-based resists, are not stable to the plasma etching processes used for semiconductor structuring. In turn, however, the methacrylates are not sufficiently sensitive.
The polymers having the highest radiation sensitivity known to date for electron beams or X-rays are polyalkene sulfones, in particular, polybutene-1-sulfone. The disadvantage of this class of compounds is, however, that they are less resistant to plasma etching processes; they are therefore suitable for mask production, but not for semiconductor fabrication using a mask made of this material. It has therefore been proposed to combine polyalkene sulfones with novolak resins, which, as is generally known, are resistant to plasma etching (M. J. Bowden et al., J. Electrochem. Soc., 128: 1304 (1981); U.S. Pat. No. 4,289,845). However, it became apparent that the two polymers are extremely incompatible with one another, thus impairing the resolution. An attempt to improve the compatibility by admixing further components resulted in loss in sensitivity (U.S. Pat. No. 4,398,001).
Photocatalytic systems are described in DE-A-2,718,254 and DE-A-2,928,636 for use with electron-beam and X-ray radiation. In these positive systems, chlorine-containing compounds, in particular, of the substituted triazine type, are employed as compounds which form an acid under the action of actinic radiation. During structuring of these materials using electron or X-ray radiation, however, it became apparent that the edges of the resist structures are very negatively undercut after development (edge angle around 60.degree. according to a photomicrograph using a scanning electron microscope (SEM)) and structures of less than about 2 .mu.m can consequently no longer be resolved or reproduced or, in other cases, are extremely frayed.
In DE-A-2,928,636, as in DE-A-2,610,842, 2,3,4,5-tetrachloroaniline, inter alia, is mentioned as the chlorine-containing compound. In addition, DE-A-2,610,842 also discloses compounds which contain aliphatically-bound bromine and one compound which carries aromatically-bound bromine: 2,2',4,4',6,6'-hexabromodiphenylamine. However, it has been shown that adequately high resolution cannot be achieved using the aromatic chlorine compound, and undesired scumming occurred with the compound mentioned containing aromatically-bound bromine.